FIG. 1 and FIG. 2 are an overall plan view showing a general example of HDD, and an enlarged view of its essential portion, respectively. For example, three magnetic disks 3 as recording medium, laid coaxially one upon another at equal distances on spindle axis 2, can rotate in housing 1. A magnetic head (not shown in the drawings) for writing/reading information on/from magnetic disks 3 is fixed to the tip end of head arm 4. The base end of head arm 4 is pivotally supported on pivot axis 5 to make a rotary motion. Head arm 4 supports such parts as a suspension, a slider, a lifting feature, etc. The magnetic head fixed to the underside of the slider is kept on standby at a position away from magnetic disks 3, while retained by ramp structure 6, when HDD is out of operation (unloading time).
When HDD is put into operation (loading time), and when magnetic disks 3 reach a given revolution rate after starting to operate, head arm 4 makes a counterclockwise rotary motion shown by arrow mark X in FIG. 1 around pivot axis 5 to release the magnetic head from ramp structure 6, which has so far held the magnetic head, and to make the magnetic head move towards magnetic disks 3. The magnetic head is levitated to a height of a few μm from the surface of magnetic disks 3 and stayed there to conduct writing/reading of information.
In the case of the HDD loading in portable computers such as so-called lap-top personal computers or note-type personal computers it sometimes occurs that head arm 4 moves unpreparedly toward magnetic disks 3 particularly due to impacts or vibrations, especially during carrying, so that the magnetic head so far kept on standby may be released from ramp structure 6. As a result, it sometimes occurs that the magnetic head is brought into contact with the surface of magnetic disks 3 or stuck thereon to damage both of magnetic head and the magnetic disks, leading to erasing of recorded information.
To prevent such troubles, latch mechanism 10 as shown within circle C in FIG. 1, is provided as a stopper means to prevent unprepared movement of head arm 4 so as not to release the magnetic head from ramp structure 6 even if an external force due to impacts or vibrations acts on HDD.
As is apparent from the enlarged view shown in FIG. 2, latch structure 10 can release or control rotary motion of head arm 4 through abutment on locking pawls 4a and 4b provided on both sides of base edge of head arm 4. That is, latch structure 10 provides longer link member 11 capable of minute rotary motion such as a rocking motion in an counterclockwise direction A and in a clockwise direction B, while being pivotally supported by hinge pin 11a as a pivot shaft; first shorter link member 12 abutting on one projection 11b provided on the tip end portion of link member 11; second shorter link member 13 abutting on another projection 11c and leaf spring 14. Thus, all these members are released in case of HDD loading, thereby enabling counterclockwise rotary motion of head arm 4, whereas in case of HDD unloading all these members are engaged with locking pawls 4a and 4b of head arm 4, thereby inhibiting such a movement of head arm 4.
However, when HDD is subjected to relatively large external impact forces, such latch mechanism 10 can control the movement of head arm 4 correspond to the external force, but when the external impact force is very small, the response of longer link member 11 having a complicated shape in particular is not sharp among the structural members, because link member 11 has been so far made from resins and thus is light in weight. To increase the weight it would be possible to shift the materials of link member 11 from resins to metal, but production of such a longer link member having complicated shape as shown in FIGS. 1 and 2, by mechanical processing such as press molding, etc. is not so easy, because of very complicated fabrication of molds, etc. for such working, and also because of an increase in the resulting production cost as a problem.